Which command allows you to run a command in an already running container?

The command that allows you to run a command in an already running container is "docker exec." This command is specifically designed for executing a new command inside an active container. When you use it, you can start an interactive shell or execute a specific command without needing to restart the container or create a new one. This is particularly useful for managing processes and troubleshooting within a running container.

For example, if you want to open a bash shell in a running container, you can utilize "docker exec -it /bin/bash." This capability is crucial for performing tasks like inspecting files, modifying configurations, or running administrative commands directly within the context of that container.

Other commands serve different purposes. "docker attach" connects your terminal to a running container's process, allowing you to interact with it, but it doesn't let you run new commands. "docker run" is used to create and start a new container based on an image, which is not applicable if you're looking to work within an already existing container. Lastly, "docker start" is used to start a stopped container, which does not imply executing any commands within it. Thus, "docker exec" is essential for executing commands directly inside an already running container environment.